he moment we believe we are saved ... Romans 10:9 &10 says,
"because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved.
The "you will be saved" does not mean that one day, sometime in the future, you will be saved, no, Paul immediately follows it up with,
"For with the heart one believes and is justified, and with the mouth one confesses and is saved".
"Is justified ... "is saved", right there and then ... I "is" justified and I "is" saved", not great English but you get the drift.
So salvation occurs when the believing one confesses Jesus Christ as Lord, then blammo it happens.
John adds the approach that by believing in his name (his name - which simply means in the person), is to "receive him".
So when did I receive him ?
When I believed in the person of Jesus Christ.
So what am I believing ?
The Gospel, the good news that Jesus Christ the sinless One, gave his pure life to God as a substitute for my rotten life.
A death God demanded I should have died.
My debt to God is now "paid in full" - tetalestai (Gk - paid in full).
In those days when you owed someone money they would nail a note on your door stating how much money you owed and when the debt was paid up
in full, they would nail another note using the word "tetalestai", paid in full.
Just before Jesus died on the cross he said "tetalestai" paid in full, and this was "nailed" over the door of every persons life debt they owed to God.
Hallelujah, we don't owe God anymore

And this debt cancellation with God happened at the very same time I accepted his gift of grace Jesus Christ by me believing in Christ and what He did
on the cross.
I definitely agree that "the good work He began in you" is the sanctifying work of the Holy spirit in our lives after believing in Christ.
Salvation is by grace through faith alone and therefore, any supposed suffering that we go through as Christians cannot be because Jesus didn't do
a complete job on the cross and now we have to make up for it by the works of suffering or enduring the world and all it throws at us.
Your verses: James 1:12, Acts 14:22.
No, if we continue steadfast through all the junk of life and don't quit it just proves that our faith in Christ is genuine and this means that our salvation
is a reality.